An image sensor is a device that converts a visual image to an electric signal. The image sensor is used chiefly in digital cameras, but may also be found in other imaging devices. The sensor is usually an integrated circuit containing an array of charge-coupled devices (CCDs) or CMOS pixel sensors, where the latter are referred to as active pixel sensors (APS).
The quality of an image produced using an image sensor may be distorted due to various noise levels introduced during capturing and producing the image. For example, as the area per active pixel element for imaging sensors shrinks, the pixel elements gather less light and may become more susceptible to current fluctuation (i.e., dark noise) generated by background radiation in a pixel element. The longer the pixel elements are exposed, in low light conditions, and the higher the amplification gain per pixel element, the more dark noise will result and cause image distortion.
Noise from random excitations of CCD or APS pixel elements may occur non-linearly over time, such as in single uncorrelated spikes or bursts of short duration. Noise from random excitations may come from the increased sensitivity of the pixels and high-energy random photons being detected in regions (e.g., the near infrared (NIR) or extreme ultraviolet (EUV)) that are not intended to be detected. For example, alpha particles or gamma ray photons can cause excitation in individual pixels. Such noise sources are high-speed, random, individual events that may typically occur in a single pixel, and account for a large fraction of total energy absorbed by the pixel in selected interval of time (i.e., frame), rather than a gradual, cumulative event.
Currently, in active pixel sensors that are controlled by row and column, it is not possible to detect a random excitation which deposits an excessive amount of energy in the pixel. To remedy this problem, a correction function is usually utilized which requires interpolation, or color channel filtering. Unfortunately, however, the data from cells that underwent excitation may be permanently lost, as a result of applying the correction function, all to the detriment of image quality.
There is a need, therefore, for methods and system to save the data that may be lost due to the above correction function to maintain a high picture quality, especially in a high-sensitivity sensor that may be subjected to high dose excitations of very short intervals.
Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects, in accordance with one or more embodiments.